| Summary: | Fertilizer sphericity is an important assessment index of appearance quality that affects the fertilization effect. A fertilizer sphericity measuring device based on machine vision was designed aimed at low precision and heavy workload of manual fertilizer measurement, and high cost and complicated operation of high precision measuring instruments. A fertilizer sphericity measuring method based on equatorial and meridian circles was proposed. The device works in an intermittent static acquisition mode to simultaneously obtain both top and side images of a single fertilizer. First, the method performs gamma correction on the top and side images of the single fertilizer, and uses the Canny operator to detect the edge of the image to obtain the equatorial and meridian circular contour images of the fertilizer. Second, based on the fertilizer equatorial and meridian circular contour, the Least Squares Circle method was used to evaluate the roundness of the single fertilizer. Finally, the average roundness value of the equatorial and meridian circles was used as the final sphericity value of the fertilizer. The sphericity measurement test was carried out on the same batch of compound, organic and biological fertilizers by using the sphericity measuring device. The fertilizer sphericity data were obtained by different measurement and evaluation methods. The variation coefficient was used to evaluate the difference in fertilizer sphericity measured by different sphericity measurement and evaluation methods. The results show that among the different measurement and evaluation methods, the coefficient of variation of fertilizer sphericity measured by the equatorial and meridian circle method was the smallest, and the coefficient of variation of sphericity measured by the Least Squares Circle method was the smallest and accurate. This study shows that the sphericity measuring device and method can accurately measure the fertilizer sphericity, and has a significant potential to facilitate fertilizer production and quality inspection.
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